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Bio 360 - Cell Biology > Topic 3 - Membranes > Flashcards

Topic 3 - Membranes Flashcards

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1
Q

In what ways can a lipid molecule in the membrane move?

A
  • lateral diffusion
  • flip-flop (flipases) – rare and slow
  • rotation
  • flexion
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2
Q

What are key features to Phospholipids and give one example

A
  • consist of 2 fatty acid chains, saturated or unsaturated
  • glycerol back bone
  • phosphate group (negatively charged)
  • and an X group (could be anything); choline, serine, etc.
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3
Q

Give 3 examples of phosphoglycerides

A
  • phosphatidylcholine
  • phosphatidylethanolamine
  • phosphatidylserine
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4
Q

Sphingolipids, what makes them different from phosphoglyceridse?

A

consist of a sphingolipid fatty chain, fatty acid tail, phosphorous group, and an X group

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5
Q

Explain the role of sterols in the membrane?

A
  • have a rigid ring structure as a head group attached to a non-polar hydrocarbon tail
  • these sterols increase the membrane flexibility and fill in any gaps from unsaturated fatty acid chains
  • flip flop across the membrane
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6
Q

Glycolipids explained, with 2 examples?

A
  • galactocerebroside; ganglioside

- oligosaccharide groups are attached to the polar head groups (typically only on the extracellular side)

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7
Q

What are the differences between Bacterial Lipids and Archaea Lipids? and some key points about archaeal lipids?

A
  • bacteria have ESTER linkages between the head groups and hydrophobic core
  • Archaea have ETHER linkages between the head groups and hydrophobic core
  • Archaea will also have isoprenoid side chains that are branched and have monolayers where two heads groups are attached to on hydrophobic chain
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8
Q

Compare the variety of lipids between eukaryotes and prokaryotes.

A

Eukaryotes may have up to 500 different lipids in a membrane compared to only one major lipid type in prokaryote (who also lack cholesterol)

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9
Q

Where is cholesterol only found?

A

Animals, plants, and fungi

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10
Q

How does unsaturated fatty acids help with packing in a lipid bilayer? (in regards to change in temperature and ratio)

A

The ratio will be higher for unsaturated to saturated fatty acids as the temperature drops - this is to keep the membrane more fluid at cooler temperatures - this is when saturated lipids become rigid

  • unsaturated fatty acids prevent tight packing
  • the cis double bond keeps the membrane fluid
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11
Q

What enzyme is active at the membrane lipids when the temperature drops?

A

Desaturase: will change the portion of unsaturated lipids to increase the ratio of unsaturated fatty acid chains

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12
Q

Can you find phospholipid monolayers in cells?

A

Yes; these will be used for storage

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13
Q

Give 7 examples of different membrane proteins

A
  • single pass via alpha helix
  • multipass via alpha helix
  • beta barrels
  • only associated with the cytosolic side as a monolayer (alpha helix is integrated however though)
  • protein anchored to a lipid anchor
  • protein attached to a GPI inside the ER lumen (glycosylphosphatidylinositol)
  • attached through non-covalent interactions
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14
Q

What is a hydropathy plot used for? and how do transmembrane proteins integrate themselves into a membrane?

A
  • these plots are used to determine the number of transmembrane components of a protein
  • a multipass protein will first integrate itself into the membrane before folding itself into the correct shape
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15
Q

What is the function of the Beta-sheets?

A
  • functioning like a pore: located on the outer membrane of mitochondria, chloroplasts or bacteria
  • these will be hydrophillic on the inside of these channels allowing hydrophobic molecules to pass through
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16
Q

How does the association of proteins with the membrane affect the function of proteins (2)

A
  • if these are transmembrane proteins they will be able to interact with both sides of the membrane
  • these proteins will be not able to function as a transporter, receptor, or channel
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17
Q

What are 3 different bond types that allow proteins to bind to lipid anchors?

A
  • amide linkage
  • thioester linkage
  • thioether linkage
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18
Q

What purpose do glycoproteins have on membrane bound proteins?

A
  • these sugar will only be attached to the proteins on the extracellular side
  • these oligosaccharides may be branched
  • and will serve as a site for cell-cell interactions & for physical protection
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19
Q

What technique would you use to measure protein mobility in a given normal cell?

A

FRAP

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20
Q

How can proteins be motile along the membrane?

A
  • Some proteins may aggregate to certain regions in the cell by interacting with other cytoskeletal or extracellular proteins
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21
Q

What are lipid rafts? and what do they entail for the membrane

A
  • aggregation of special lipids and proteins in certain areas
  • these proteins may be slightly thicker or bigger and require more room in the membrane (this means there may be a higher [ ] of sphinolipids, sterols, and glycoproteins in the membrane)
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22
Q

What does having sphinolipids, sterols, and glycoproteins in the cells membrane mean?

A
  • this will increase the surface area and lead the membrane to stretch
  • the increased size of the head groups may accumulate in an area and bending/shaping the membrane
23
Q

What do membranes create? & explain the difference between chemical & electrical gradients

A

Cells and organelles - though compartments

  • electrical gradient is based on charge
  • a chemical gradient is based on concentration
24
Q

How do cells exchange molecules across the membrane?

A
  • Hydrophobic small molecules: diffusion
  • inorganic ions, small organic polar molecules: channels and transporters
  • macromolecules: vesicles
25
Q

Give an example of a hydrophobic molecules that requires diffusion?

A

O2, CO2, N2, steroid hormones

26
Q

Give an example of inorganic ions, small polar molecules that require channels and transporters?

A
  • H2O, glycerol, urea, NH3
  • glucose, sucrose
  • H+, Na+, HCO3-, K+, Ca2+, Cl-, Mg2+
27
Q

How do macromolecules get across a membrane?

A
  • via either endo or exocytosis
28
Q

Explain the differences and types of transport: diffusion, passive transport and active transport

A
  • there will always be a chemical, electrical or electrochemical gradient
  • Active transport: requires an input of energy
  • passive transport will always be channel mediated or through conformational changes
29
Q

What is a transporter? and transporter-mediated diffusion?

A
  • an enzyme reaction that causes a conformational change and release on the other side
  • will follow a saturation curve (a limit can be reached)
30
Q

What is a channel?

A

functions as a door - never binding anything simply opening and closing

31
Q

What are 3 types of active transport systems? with a fact and examples

A
  • coupled transporter (can either be a symporter or antiporter – meaning a piggy back transport or a one in, one out situation – ex. Na+ cotransport vs Na+ H+ antiporter)
  • ATP driven pump - causes conformational changes
  • light driven pump
32
Q

What are the 3 types of ATP pumps? - where would each one be used?

A
  • P-type pump (Ca2+ or Na+/K+ pump)
  • ABC transporter (ATP Binding Cassete - bacteria use this as unidirectional pump, eukaryotes is both ways)
  • V-type proton pump and F-type ATP Synthase (pump H+ against the gradient OR form ATP - in mitochondria)
33
Q

Explain how glucose would transport into a cell and out of a cell, explaining gradients and cotransport

A
  • low [ ] glucose outside the cell, so ACTIVE transport is required, Na+ piggy backs on using a symporter
  • once inside the cell low [ ] glucose outside the cell so a PASSIVE transport will be used
34
Q

Explain in short how a Ca2+ Pump works and what class of pump it is?

A
  • P Type ATPase
  • located in the sarcoplasmic reticulum
  • side open to the cytosol when an ATP is bound - this allows a Ca2+ to bind causing a conformational change closing the activated domain (through the phosphorylation of the ATP –> ADP)
  • a second ATP binds removing the first ADP leading to the opening of the pump @ the sarcoplasmic side
  • Ca2+ is released and 2H+ ions takes its place and closing the pump again
  • phosphorylation domain is phosphorylated opening the pump releasing the 2 H+ and the cycle starts all over again
35
Q

Explain in short how a Na+-K+ Pump works and what class of pump it is?

A
  • a P-type ATPase
  • there is a low [ ] of Na+ in the cell
  • first 3Na+ binds the active site from the cytosolic side, the pump binds ATP which is then phosphorylated causing a conformational change
  • ADP is removed causing another conformational change releasing the 3Na+ on the extracellular side and taking up a 2K+
  • 2K+ bound at the binding site releases the phosphoryl group causing a conformational change releasing the 2K+ on the cytosolic side and the cycle repeats
36
Q

How does an ABC Transporter work, and what does it stand for?

A
  • ATP Binding Cassete Transporter
  • a solute binding site binds a small solute molecule
  • 2 ATP’s bing at the ATPase domains allowing this solute binding to occur, phosphorylation of them both cause a conformational change and the molecule is released on the other side
37
Q

What are 4 characteristics of ion channels?

A
  • high ion selectivity
  • pores are gates
  • high efficiency
  • ALWAYS PASSIVE transport
38
Q

There are 4 different channels based on how they open up, what are they?

A
  • voltage gated
  • ligand-gated (extracellular ligand)
  • ligand-gated (intracellular ligand)
  • mechanically gated: stretch in the membrane which opens a pore
39
Q

How does a mechanosensitive channel work?

A
  • through osmotic stress regularity of the cell
  • the membrane will stretch which opens up a channel from this force (ex. outflow of iron, which decreases this pressure)
40
Q

How is membrane potential in animal cells created? And how do ion channels create selectivity with high conductance?

A
  • HIGH Rate & Selective for passive pressure

- cytosolic side is typically negative while the extracellular side is more negative

41
Q

How is the Na+/K+ ATPase involved in membrane potential?

A

This pump typically pumps 3 Na+ out of the cell and pumps 2 K+ into the cell - thus leaving a more negative charge inside the cell
- this creates and electrochemical gradient for Na+ inside the cell and K+ outside the cell

42
Q

What is the K+ leak channel?

A
  • K+ has a leak channel for passive diffusion to balance its chemical gradient, where this is maintained to keep the membrane potential and preventing the cytosolic side from becoming to positive
43
Q

What are the key features of the K+ channel?

A
  • there is an internal negative charge for the pore and the vestibule which will attract the positively charged K+ and Na+
  • the vestibule has not role in selectivity
  • the selectivity channel narrows and controls the channels selectivity by being aligned by carbonyl groups
44
Q

What is the purpose of the carbonyl groups in the K+ channels selectivity filter?

A

When K+ is transported it is surrounded by a hydration shell
- once it reaches the selectivity filter the carbonyl groups will strip the hydration shell and K+ fits perfectly through

45
Q

Why can a smaller molecule such as Na+ not filter through the K+ channel?

A
  • being a smaller ion, also covered in a hydration shell, it will not be able to interact with all the oxygen molecules in the selectivity filter and does not have enough energy to strip the cell (to strip the hydro shell is energy dependent) - thus it is not energetically favourable to strip the water shell
46
Q

Compare now a K+ channel to a Na+ channel

A

These channels are large enough to allow Na+ with its hydro shell to pass through the channel, however the larger K+ ion with its hydro shell will be too large to pass through

47
Q

Aquaporins structure?

A
  • tetramer with a pore in the middle
  • one side of the pore is hydrophilic while the other is hydrophobic
  • this pore is too small for any hydrated ions to pass through
  • water will NOT interact with the hydrophobic side, while stripped ions will not fir through either
  • Two hydrophilic amino acids in the middle of the pore line one side determine whether or not the molecules will pass through but interact with the H2O
  • the H2O pass through the pore by making and breaking hydrogen bonds with the hydrophilic side (this prevents H+ ions from passing through the membrane)
48
Q

What is the structure of a voltage-gated channel?

A
  • one polypeptide domain
  • an alpha helix which contributes the channel and central pore
  • the lateral portal is for key entry points for small hydrophobic drugs
49
Q

Why is there an inactivation gate, is the inactive state important then?

A
  • to control and limit the time period for how long the channel will remain open
50
Q

What are the 3 possible states of a Na+ voltage gated channel?

A
  • closed, open, inactive
  • the plasma membrane at rest will have a positive extracellular potential will the cytosolic side and a negative potential - meaning the channel is closed
  • a voltage sensor on the channel will determine when to open and activate; typically when the channel is depolarized (OPEN - positive on the cytosolic side and negative on the extracellular side)
  • the inactivation will because by the inactivation gate swinging a handle into the channel blocking any movement
51
Q

How does depolarization occur in a Na+ Voltage-gated channel?

A
  • the signal will only propagate in one direction due to the inactivation & RE-POLARIZATION of the neighbouring channels
52
Q

How do you analyze the voltage-gated channels? and what does aggregate current refer to?

A
  • Through the patch clamp technique
  • measure the current through the channels, as the signal is passed through the channels the signal will aggregate and increase in strength as more cells activate
53
Q

What are transmitter-gated ion channels? and what are two different types with examples?

A
  • highly selective binding sites for a neurotransmitter
  • excitatory neurotransmitters: acetylcholine & glutamate (both opening sodium channels)
  • inhibitory neurotransmitters: GABBA & glycine (these will open Cl- and K+ channels to increase the NEGATIVE charge in the cell and return the membrane potential levels)

Bio 360 - Cell Biology (10 decks)

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